The unprecedented rise in cost of energy in the United States over the last decade due to the OPEC countries' price control of petroleum has resulted in the cost of energy, especially electrical energy, being increased over fivefold.
Caustic soda and chlorine are produced by the electrolysis of an aqueous solution of sodium chloride in various types of electrolytic cells. Major tonnages of caustic and chlorine were made by the mercury cell process; however, because of pollution and environmental problems, this process, although still used, is giving way to other cell processes which allow for better economics and avoid the mercury pollution problems. Diaphragm cells employ asbestos diaphragms, and since asbestos has become an objectionable pollutant, processes have been developed for stabilizing the asbestos by use of fluoropolymer reinforcements. The latest type of cell, the ion exchange membrane cell which is now being installed for commercial use, avoids many of the objections of the prior chlor-alkali cells.
The cost of producing chlorine and caustic soda by the process which involves electrolyzing salt contained in concentrated brine has been a significant contributor to the rising cost of most consumer materials using chlorine or caustic soda during the course of their manufacture. Significant contributions in lowering the amount of electrical energy necessary for the electrolysis of salt have been made with the introduction of dimensionally stable anodes for use in chlor-alkali cells as a replacement for graphite anodes. Still another significant contribution in lowering the electrical energy costs in the manufacture of chlorine and caustic by the electrolysis of salt has been made by the introduction of ion exchange membrane separators for use in place of asbestos or modified separators. The introduction of chlor-alkali membrane cells which now employ dimensionally stable anodes has caused a further search to improve their energy efficiency. For example, catalytic surfaces for use on the cathodes of chlor-alkali electrolytic cells are being developed. An additional area for realizing cost improvement in the manufacture of chlorine and caustic in membrane cells is in the handling and treatment of the salt, which is a basic raw material required in the electrolysis process.
This invention relates to new and novel processes and systems for treating and handling the brine and salt solutions in the process of making chlorine, caustic and hydrogen in ion exchange membrane electrolytic cells and the resultant plant installations.